Motor structure and their manufacturing method

ABSTRACT

The motor structure, which has a laminated structure of plural plates  1  and also has a stator pole assembly  10  formed with a component mounting portion, comprises a synthetic resin layer  6  which encloses and covers the plural plates  1  while holding the plates in a closely contacted state, overhang portions ( 8, 9 ) integral with the synthetic resin layer  6  and which serve to not only hold but also position motor components, and an insulating film  7 ′ which covers portions not coated with the synthetic resin. While the synthetic resin layer is formed on the surface of the lamination stack, pressure is applied to the laminated plates as constituents of the stator pole assembly from both upper and lower surfaces of the laminate. This application of pressure is performed using plate pressing projections formed in the mold.

This application is a divisional of application Ser. No. 09/069.951,filed Apr. 30. 1998, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor structure and a method formanufacturing the same. Particularly, the invention is concerned with amotor structure and a method for manufacturing the same which motorstructure and method permit easy insulation of stator poles formed bylamination of soft magnetic plates and easy mounting of components tothe stator poles.

2. Description of the Prior Art

Small-sized synchronous motors and stepping motors are used as drivesources of various electronic devices such as floppy disk drives whichare peripheral devices of personal computers. As an example of thesemotors there is known an inner rotor type motor in which a cylindricalrotor comprising poles of permanent magnets is disposed rotatably, andmagnetic poles of a stator for generating a rotating magnetic field andthereby imparting a driving force to the rotor are disposed around therotor in a face-to-face relation to the rotor. The stator poles arefixed to a substrate constituted by an insulated metal plate, while therotor is supported by two bearings which are fixed respectively to thesubstrate and the stator poles. Onto the substrate are further fixed anelectronic circuit for driving the motor, as well as components such asa position detecting coil for detecting the position of the rotor.

There also is known an outer rotor type motor in which a plurality ofmagnetic poles are projected radially from an annular yoke member andstator coils are wound round those magnetic poles to constitute statorpoles, which stator poles are fixed to a substrate, while a shallowdish-like, or tray-like, rotary disk is disposed rotatably around thestator poles, and permanent magnets disposed inside the edge of therotary disk are made face to face with the front ends of the statorpoles.

According to the prior art, in fabricating the stator poles, no matterwhich type of motor may be concerned, a plurality of plates formed bypressing from a soft iron plates are stacked together to constitute alamination stack, then for ensuring insulation between the laminationstack and a coil wound round the stack, an insulator is formedseparately using an insulating material such as resin for example and isinserted into the coil winding portion of the lamination stack, or aninsulating paint is sprayed directly to the lamination stack to form athin insulating film on the whole surface of the lamination stack, orthe lamination stack is subjected to a chemical treatment to form aninsulating film on the surface thereof.

As mentioned above, the conventional assembling method involvingseparately forming an insulator for the lamination stack, inserting itbetween magnetic poles and winding a coil thereon, is expensive becauseof separate formation of the insulator and requires additional number ofsteps for assembling the insulator.

In the above formation of the insulating film by spray coating, it isimpossible to form an insulating film having a uniform thicknessthroughout the whole surface of the lamination stack. Particularly,corners and edges are apt to be insufficient in thickness, which maycause dielectric breakdown during use of the motor. Further, in therecent assembling work for a smallsized motor, there is no space forclamping the whole of a pressed plate with pressure using eyelet or thelike, with no clamping pressure exerted on the front-end peripheral edgeof a stator pole tooth 100, as shown in FIGS. 6 and 7. Consequently,there occurs a gap between adjacent laminated plates of the assembledmotor, and the plates are rusted in their interiors when used over along years. Besides, when the stator is excited or the rotor is rotated,the plates vibrate and generate noise. There is an additionalinconvenience such that bearing parts and other motor constituting partsmust be mounted one by one to the substrate at the time of assembly. InFIGS. 6 and 7, the numeral 101 denotes a lamination stack whichrepresents the whole of a stator pole, numeral 102 denotes a yokeportion, numeral 103 denotes a caulking portion for clamping plates 104,and numeral 105 denotes a coating surface which coats the laminationstack 101 in the spray method.

SUMMARY OF THE INVENTION

The present invention intends to eliminate the above-mentionedinconveniences of the prior art and it is an object of the invention toprovide a novel motor structure and method for manufacturing the samewhich, when laminating plates as constituents of a lamination stack, canclamp the plates hermetically under pressure and can mount components ofthe motor to the lamination stack before mounting the motor to asubstrate or the like.

According to the present invention, in order to achieve theabove-mentioned object, there is provided a motor structure having alaminated structure of plural plates and also having a stator poleassembly formed with a component mounting portion, the motor structurecomprising a synthetic resin layer which encloses and coats the pluralplates in a closely contacted state of the plates, an overhang portionintegral with the synthetic resin layer and which serves to not onlyhold but also position motor components, and an insulating film whichcovers a portion not coated with the synthetic resin layer. There alsois provided a method for manufacturing a motor structure having alaminated structure of plural plates and a stator pole assembly formedwith a component mounting portion, characterized in that a syntheticresin layer is formed on the surface of a lamination stack under theapplication of pressure from both upper and lower surfaces of thelaminated plates which constitute the stator pole assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial front view of a motor's stator pole of thisinvention;

FIG. 2 is a partial sectional view of a motor's stator pole of thisinvention;

FIG. 3 is a partial front view of an exposed position adhered with aninsulating film;

FIG. 4 is a partial sectional view of an exposed position adhered withan insulating film;

FIG. 5 is a sectional view of assembled motor structure applied thisinvention;

FIG. 6 is a partial front view of prior art; and

FIG. 7 is a partial sectional view of prior art as seen along line I—Iof FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described in detailwith reference to the accompanying drawings. FIGS. 1 and 2 are a partialfront view and a partial sectional view, respectively, showing a statorpole used in a motor structure embodying the present invention. In thesefigures, the numeral 1 denotes a plate as a constituent of the statorpole. The plate 1, which is a soft magnetic plate, has an annular yokeportion 2, stator pole portions 3 projecting in a plural number radiallyoutwards from the yoke portion 2, and stator pole teeth 4 formedrespectively at the tips of the stator pole portions 3. Plural suchplates 1 are laminated together and are caulked at a nearly centralportion 5 of each stator pole portion 3. In this state, gaps are formedbetween stator pole teeth 4, 4 and also between yoke portions 2, 2 ofadjacent laminated plates because the tip portions of the stator poleteeth 4 and the yoke portions 2 are not vertically pressed. This problemwill be solved if these portions are each formed with a caulking portionas is the case with the stator pole portion 4. However, there is nospace for the provision of such fixing means. It also may be onesolution to spot-weld the whole of the plates in the thicknessdirection. However, this method is inconvenient because there will occuran eddy current loss.

In this embodiment, in view of the above-mentioned points, a mold isprovided so that a lamination stack constituted by laminating the plates1 is coated with a synthetic resin material. Projections for pressingthe stator pole teeth 4 and the yoke portions 2 of the laminated platesfrom both upper and lower surfaces are formed beforehand within themold. The lamination stack is loaded into the mold and the syntheticresin is poured into the mold to form a thin synthetic resin layer 6 onthe surfaces of yoke portions 2, stator pole portions 3 and the statorpole teeth 4. Further, spaces for forming portions to fix suchcomponents as bearings are formed beforehand in the mold. Therefore, astator pole assembly after the molding is provided with the saidportions, namely overhang portions for not only holding but alsopositioning motor components. In this embodiment, as shown in FIG. 2,there are formed a circular groove 8 for loose fitting therein of arotor hub as will be described later and a projection 9 for positioninga stator pole assembly 10 with respect to a substrate.

In this embodiment, since the stator pole teeth 4 and the yoke portions2 are pressed from both upper and lower surfaces by means of projectionsduring molding and in this state the synthetic resin is poured into themold, the plates when taken out from the mold are in a mutually closelycontacted state. But there appear exposed portions 7 is not coated withthe synthetic resin. Also at the portions which have been in contactwith the inner wall of the mold there appear exposed portions 7 andcaulking portions 5 not coated with the synthetic resin.

Further, there sometimes appear surface portions partially not coatedwith the synthetic resin when the resin does not spread uniformly (shortmold), for example, when the resin flowing condition changes duringmolding or when there occurs a positional deviation upon loading of thelamination stack into the mold.

In this embodiment, as shown in FIGS. 3 and 4, the exposed portions 7and the caulking portions 5 not coated with the synthetic resin arecoated with an insulating film 7′ of a synthetic resin or the like byelectrode position coating or by spray coating. More specifically, forexample, the whole of the stator pole assembly 10 after taken out fromthe mold is put into a coating solution tank and is electrically chargednegatively, then fine particles of a coating material, which is apositively charged insulating material, are adsorbed on the exposedportions 7 and caulking portions 5 not coated with the synthetic resin.For example, after the stator pole assembly 10 has been chargednegatively, if fine particles of the positively charged insulatingmaterial as the coating material are sprayed as fine bubbles toward thestator pole assembly 10, the bubbles of the coating material will beconcentrated and adsorbed on the exposed portions 7. Upon subsequentdrying of the coating material thus applied, all the exposed portions onthe surface of the stator pole assembly are covered with the insulatingfilm 7′ formed of the coating material.

FIG. 5 is a sectional view of the motor structure using the stator poleassembly to which the present invention was applied. The motor isassembled by fitting the projection 9 into a positioning hole 12 formedin a substrate 11, the projection 9 projecting below the stator poleassembly 10 with a stator coil 13 attached thereto, then fixing thestator pole assembly 10 onto the substrate 11 with use of a fixing means(not shown), thereafter fitting bearings 15 and 16 on a support shaft 14erected on the substrate 11, and further fitting a rotor 17 on the outerraces of the bearings 15 and 16. In this motor, a hub 18 which holds thebearings of the rotor 17 is loosely fitted in a non-contact manner intothe groove 8 formed inside the stator pole assembly 10. A terminal 19connected with the stator coil 13 is attached through the projection 9.

Although the present invention has been described above by way of anembodiment thereof, various modifications may be made within the scopeof the gist of the present invention. For example, there may be adopteda method in which the stator pole portion 3 is loaded into the mold sothat the whole of the outer peripheral surface of the stator poleportion 3 is in contact with the inner wall of the mold and in which theouter peripheral surface of the stator pole portion 3 not coated withthe synthetic resin during molding is subjected to an insulating rustpreventing treatment by electrode position coating or by spraying acoating material consisting principally of a special silicate and acomposite resin to a thickness smaller than the thickness of theinsulating film 7′ after molding. By forming such a thin film on thewhole outer peripheral surface of the stator pole portion 3, it ispossible to diminish the gap between the said outer peripheral surfaceand the inner peripheral surface of the magnet and hence it is possibleto further improve the motor torque. Additionally, by contacting thewhole outer peripheral surface of the stator pole portion 3 with theinner wall surface of the mold, the positioning of the stator poleassembly 10 with respect to the mold becomes more accurate, the state ofshort mold due to eccentricity is remedied and a mechanical accuracysuch as coaxialness is improved. These modifications and applicationsare not excluded from the present invention.

In the present invention, as set forth above, since the stator poleportion of the stator pole assembly is covered with an insulating film,a coil can be wound directly round the stator pole without the need ofusing a bobbin or the like. Thus, the assembling work becomes simplerand the cost is reduced. Since the insulating layer of the syntheticresin which covers the whole of the lamination stack holds the plates inclose contact therewith without forming any gap between adjacent platesand provides a hermetic seal, there is no fear of the plates vibratingand generating noise during use, nor is there any fear of rusting on theplanar portion of each plate. Moreover, for example a portion for themounting of other components such as terminals and a positioning portionto be used at the time of mounting the stator pole assembly to thesubstrate can be formed in the stator pole assembly accurately in asimple manner. Consequently, it is possible to assemble the motor in asimple and accurate manner. Further, since all of the exposed portionsformed at the time of covering the stator pole with the insulating filmof the synthetic resin by molding are covered with an insulating film,it is possible to improve the electric insulation performance.

What I claim is:
 1. A method for manufacturing a motor structure havinga laminated structure of a plurality of plates and a stator poleassembly formed with a component mounting portion, comprising: preparinga plurality soft iron plates each having an annular yoke portion, and aplurality of stator pole portions which project radially outwardly fromthe yoke portion and stator pole teeth formed at an end portion of eachstator pole portion; stacking the plurality of soft iron plates; settingthe stacked soft iron plates into a mold; pressing both upper and lowersurfaces of the stacked soft iron plates by protrusions which are formedin the mold; injection molding a synthetic resin into the mold to covera portion of the stacked soft iron plates including an outer peripheralsurface of the stator pole teeth, and binding the stacked soft ironplates to each other with the synthetic resin layer and integrallyforming a circular groove and a projection formed integrally with thesynthetic resin layer to hold and position components of the motor, thecircular groove being located at a first end of the inside of the yokeportion, and receiving a motor hub component of the motor, and theprojection being formed circularly and being located on a second end ofthe inside of the yoke portion, opposite the first end of the inside ofthe yoke portion, a center of the projection forming a hole tocommunicate the interior of the hole with the circular groove, and theprojection fitting into a positioning hole in a substrate to positionthe pole assembly into the substrate ; and covering a portion of thestacked soft iron plates not covered with the synthetic resin layer withan insulting film.
 2. A method for manufacturing a motor structureaccording to claim 1, wherein said protrusions press on the stator poleteeth portions and the yoke portion during molding.
 3. A method formanufacturing a motor structure according to claim 1, further comprisingforming said insulating film with an electrode position coating.
 4. Amethod for manufacturing a motor structure according to claim 1, furthercomprising forming said insulating film with a spray coating.
 5. Amethod for manufacturing a motor structure according to claim 1, furthercomprising forming said insulating film thinner than said syntheticresin layer.
 6. A method for manufacturing a motor having a stator poleassembly formed with a component mounting portion, comprising: stackinga plurality soft iron plates, each of said soft iron plates having anannular yoke portion, a plurality of stator pole portions which projectradially outwardly from the yoke portion, and stator pole teeth formedat an end portion of each stator pole portion; setting the stackedplurality of soft iron plates into a mold; pressing upper and lowersurfaces of the stacked soft iron plates by protrusions formed in themold; injecting a synthetic resin into the mold to cover a portion ofthe stacked soft iron plates including an outer peripheral surface ofthe stator pole teeth, and to bind the stacked soft iron plates to eachother with synthetic resin layers while integrally forming a projectionportion with the synthetic resin layer for positioning the stator poleassembly; and covering any portion of the stacked soft iron plates notcovered with the synthetic resin layer with an insulating film.
 7. Amethod for manufacturing a motor structure having a laminated structureof a plurality of plates and a stator pole assembly formed with acomponent mounting portion, comprising: preparing a plurality soft ironplates each having an annular yoke portion, and a plurality of statorpole portions which project radially outwardly from the yoke portion andstator pole teeth formed at an end portion of each stator pole portion;stacking the plurality of soft iron plates; setting the stacked softiron plates into a mold; pressing both upper and lower surfaces of thestacked soft iron plates by protrusions which are formed in the mold; p1injection molding a synthetic resin into the mold to cover a portion ofthe stacked soft iron plates including an outer peripheral surface ofthe stator pole teeth, and binding the stacked soft iron plates to eachother with the synthetic resin layer and integrally forming a projectionportion with the synthetic resin layer for positioning the stator poleassembly; and covering a portion of the stacked soft iron plates notcovered with the synthetic resin layer with an insulting film.